1. Field of Invention
This invention relates to a radome for use on board an aircraft, and more particularly to a retractable radome for use with a retractable radar antenna.
2. Description of the Prior Art
The use of radar searching equipment on board aircraft requires rotatable antenna assemblies for scanning through 360.degree. of azimuth, or through some smaller sector therewithin. In order to prevent interference with the radar transmission by the body of the aircraft, it is necessary to extend the antenna some distance from the aircraft body while the scanning operation is performed. However, the aerodynamic turbulence created by an antenna structure projected from the aircraft body is substantial even for relatively slow flying aircraft, such as a helicopter. The aerodynamic effect upon the aircraft caused by the antenna structure is such as to produce a drag effect which varies with the size of the antenna reflector and the change in position of the antenna as it scans through the sector. The change in drag caused by the antenna rotation further produces a cyclic, aerodynamically induced torque about the antenna axis, which induces substantial, cyclic, pitch and roll moments about the aircraft as the antenna rotates, affecting aircraft stability and handling in forward flights at cruise and at high speeds. Furthermore, the cyclic parasite drag variations and attendant power compensation variations required to maintain a given forward flight speed may also be unacceptable.
The effect of the aerodynamic loading upon the antenna structure itself, produces severe force moments upon the antenna as it rotates through the sector. This force moment results in bearing assembly wear, and also requires that the antenna drive motor torque be programmed to accommodate the cyclic torque variations.
In view of the undesirable effects on both aircraft and antenna, it is necessary to enclose the antenna structure within some type of radome. The radome structure prevents the aerodynamic loading upon the antenna structure itself, and virtually eliminates the cyclic force moments on the aircraft due to the antenna rotation, however, the radome structure still presents a significant drag factor to the aircraft during forward flight. While such a drag effect is unavoidable during the operation of the radar system, it is desirable to further minimize the drag effect for periods of nonoperation. This may be accomplished in a radar system employing a retractable antenna structure, wherein it is permissible to use a retractable radome structure, which during periods of nonoperation may be retracted to provide a much smaller profile on the aircraft surface.